991 resultados para Radioisotopes in botany
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We briefly review the nature of light and its effects on plants, and then describe an inexpensive experimental system for studying the effects of shade, specifically the contributions of reduced intensity ("quantity") and the altered spectral distribution of foliage shade ("quantity") on the development of seedlings and other plants. This system has been devised to be safe to construct, inexpensive in its use of readily available materials, and appropriate for a range of student grade levels, from ~grade six to university courses in botany. We conclude by suggesting a range of experiments this system will allow. An advantage of this system is that it promotes the study of the responses of a large range of plants, most completely unstudied for these responses.
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The monograph is a systematic arrangement of the biographies and bibliographies of botanists in South Carolina who have contributed to the state’s reputation in botany.
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The accumulation of extraterrestrial 3He, a tracer for interplanetary dust particles (IDPs), in sediments from the Ontong Java Plateau (OJP; western equatorial Pacific Ocean) has been shown previously to exhibit a regular cyclicity during the late Pleistocene, with a period of ~100 ka. Those results have been interpreted to reflect periodic variability in the global accretion of IDPs that, in turn, has been linked to changes in the inclination of Earth's orbit with respect to the invariable plane of the solar system. Here we show that the accumulation in OJP sediments of authigenic 230Th, produced by radioactive decay of 234U in seawater, exhibits a 100-ka cyclicity similar in phase and amplitude to that evident in the 3He record. We interpret the similar patterns of 230Th and 3He accumulation to reflect a common origin within the ocean-climate system. Comparing spatial and temporal patterns of sediment accumulation against regional patterns of biological productivity and against the well-established pattern of CaCO3 dissolution in the deep Pacific Ocean leads to the further conclusion that a common 100-ka cycle in accumulation of biogenic, authigenic and extraterrestrial constituents in OJP sediments reflects the influence of climate-related changes in sediment focusing, rather than changes in the rate of production or supply of sedimentary constituents.
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no.12(1926)
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v.28 (1991-1992)
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v.20 (1978)
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v.29 (1993-1994)
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v.30 (1995-1996)
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v.21 (1979)